The present invention relates to slotted waveguide arrays, and more particularly to an array employing compound slots to provide control of the beam position.
Two types of slotted waveguide arrays in common use are the serpentine slot array and the shunt slot array. In both types of array, the waveguide must be operated at wavelengths close to the waveguide cutoff wavelength if the beam is to be tilted far off broadside. Thus, the beam is scanned as the exciting frequency is scanned.
There is therefore a need to provide a slotted waveguide array which allows the beam position to be chosen independently of the waveguide size, such that it is not necessary to operate the array at wavelengths approaching the cut off wavelength of the waveguide.
The properties of the general inclined-displaced slot (i.e., the compound slot) are described in "The Physical Principles of Waveguide Transmission and Antenna Systems," by W. H. Watson, Oxford at the Claredon Press, 1947. Watson apparently used the special properties of these slots to build a traveling wave array in which each slot could be matched with a tuning button so that the array would operate through the broadside frequency without the customary high VSWR. Insofar as is known, however, Watson did not use the phase properties of compound slots to scan the beam.
In the paper "Resonant Slots with Independent Control of Amplitude and Phase," B. J. Maxum, IEEE Trans. Antennas and Propagation, Vol. AP-8, pp. 384-389, July, 1960, a linear array is described in which the phase properties of compound slots are employed to achieve a particular shaped beam, wherein the coupling coefficients are limited to small values because of approximations involved in the analysis.
It would therefore represent an advance in the art to provide a traveling wave slotted waveguide array which allows the beam position to be chosen independently of the waveguide size, and without operating the array at wavelengths close to the waveguide cut off frequencies.
It would further be an advantage to provide a slotted waveguide array employing compound slots to achieve a desired beam position.